Pompe disease (acid maltase deficiency) is caused by a deficiency in the enzyme acid α-glucosidase (GAA). GAA metabolizes glycogen, a storage form of sugar used for energy, into glucose. The accumulation of glycogen leads to progressive muscle myopathy throughout the body which affects various body tissues, particularly the heart, skeletal muscles, liver, and nervous system. According to the National Institute of Neurological Disorders and Stroke, Pompe disease is estimated to occur in about 1 in 40,000 births.
There are three recognized types of Pompe disease—infantile, juvenile, and adult onset (see, e.g., Hirschhorn and Reuser, In: Scriver C R, Beaudet A L, Sly W, Valle D, editors; The Metabolic and Molecular Bases of Inherited Disease, Vol. III, New York: McGraw-Hill; 2001. p. 3389-420., 2001: 3389-3420). Infantile-onset Pompe Disease is the most severe, and presents with symptoms that include severe lack of muscle tone, weakness, enlarged liver and heart, and cardiomyopathy. Swallowing may become difficult and the tongue may protrude and become enlarged. Most children die from respiratory or cardiac complications before the age of two, although a sub-set of infantile-onset patients live longer (non-classical infantile patients). Juvenile onset Pompe disease first presents in early to late childhood and includes progressive weakness of the respiratory muscles in the trunk, diaphragm, and lower limbs, as well as exercise intolerance. Most juvenile onset Pompe patients do not live beyond the second or third decade of life. Adult onset symptoms involve generalized muscle weakness and wasting of respiratory muscles in the trunk, lower limbs, and diaphragm. Some adult patients are devoid of major symptoms or motor limitations.
Unless identified during pre-natal screening, diagnosis of Pompe disease is a challenge. Diagnosis of adult-onset Pompe is even more difficult since number, severity, and type of symptoms a patient experiences vary widely, and may suggest more common disorders such as muscular dystrophies. Diagnosis is confirmed by measuring α-glucosidase activity and/or detecting pathologic levels of glycogen from biological samples. Currently the only approved therapy is enzyme replacement therapy with recombinant α-glucosidase.
Pompe disease is one of several of glycogen pathologies. Others include Debrancher deficiency (Cori's-Forbes' disease; Glycogenosis type III); Branching deficiency (Glycogenosis type IV; Andersen's disease); Myophsophorylase (McArdle's disease, Glycogen storage disease V); Phosphofructokinase deficiency-M isoform (Tauri's disease; Glycogenosis type VII); Phosphorylase b Kinase deficiency (Glycogenosis type VIII); Phosphoglycerate kinase A-isoform deficiency (Glycogenosis IX); Phosphoglycerate M-mutase deficiency (Glycogenosis type X).